IL-33 is a member of the IL-1 family. It is involved in T helper type 2 response via the activation of its receptor ST2 (IL-1RL1) driving the production of Th2-associated cytokines. The stimulation of ST2 by IL-33 induces the NF-κB and MAPK pathways. The human IL-33 protein is expressed with a prodomain (aa 1-111) which is cleaved by caspase-1 to produce the 18kDa mature protein (112-270).